Plant Stem Cells

The meristem is the region of the plant that contains undifferentiated stem cells, the stem cell niche in plants. These are classified as stem cells because they fit the criteria of being self-renewing, undifferentiated, totipotent or pluripotent, and are found in a specialised area called a niche. Both plants and animals have stem cells found in niches, however, a unique feature of plant cells is that they are all totipotent. That is, if the organism were to be dealt cataclysmic damage - such as a tree being cut down to its base - it would be able to regenerate completely. This process takes place through the formation of a callus. When the plant is wounded, the differentiated cells around the wound will dedifferentiate into a group of cells, the callus, that can grow into any new organ the plant needs. Depending on the concentrations of hormones the callus is exposed to, it will differentiate into different organs. Higher concentrations of auxin lead to more root formation and higher concentrations of cytokinin lead to more shoot formation. Though it is true that an entire plant can be regenerated from a single one of these dedifferentiated cells, that does not mean all plant cells are stem cells. Stem cells must be undifferentiated and found in a niche, as such, although all plant cells can regenerate an entire organism, most of them are already differentiated and are not found in a niche.